Network distribution



Nov. 12, 1935- M. A. BOSTWICK ET AL 2,020,931

NETWORK DISTRIBUTION Filed May 19, 1954 WITNESSES INVENTQRi MyronA. Bosfwlc and 6- BerwrdE. ene

nuuiutcu LOV.

UNITED STATES PATENT OFFICE 2,020,931 NETWORK DISTRIBUTION Myron A. Bostwick, Spokane, Wasln, and Bernard 1., assignors to Westinghouse Electric & Manufacturing Comi Pany, East Pittsburgh, Pin, a

Pennsylvania corporation Application May 19, 1934, Serial No. 726,580

12 Claims.

plurality of feeders through step-down transformers from one or more supply sources. The

fiow of power between the step-down transformtransposed, 7 been rotated 120 or 240. Second, the phasing operation serves to prevent repeated opening and closing or pumping of the network switch in the event that the relationship of voltages on the feeder when the switch is closed, and closure of the switch when the latter is open. However, the second function cannot always b performed perfectly by a single network relay, and at many locations in, the network it is neces- It is an object .of our invention to provide n times of light load, and which shall remain closed during normal conditions, regardless of the magnitude or direction of powe'r'fiow.

Another object or our invention is to provide a the power simplified network system, in which directional apparatus of the prior art shall be banks in novel network protector which shall open'only when the feeder is faulted, or the feeder breakeris opened to disconnect the feeder entirely at" from the transformer more simple form of electroresponsive device substituted, which shall respond only to feeder ground faults. With such a simellminated, and a dent from the following detailed description, taken in conjunction with the accompanying drawing, in which:

Figure 1 is a diagrammatic view of a network system embodying our invention; and, 7 Figs. 2 to 7 are diagrammatic views of alternative forms of fault-responsive device which may be used in the system shown in l.

Referring to Fig. l, a grounded neutral polyphase, medium shown in the drawing.

A step-down transformer bank 4 is connected between the feeder 3 and a low-voltage distribution network 5. The transformer bank 4 is preferably connected with its high voltage windings neutral grounded,- but other arrangements familiar to those skilled in the art may be used. It is necessary, in the practice of our invention, how- 'ever, that the high-voltage windings of the transformer bank 6 be ungrounded. Although, for

simplicity, only one feeder 3 and one transformer bank 4 are shown in Fig. 1, it will beunderstood that the network 5 is supplied by means of a plurality of feeders, and each feeder is connected. to network 5 by means of a plurality of transformer accordance with the usual practice. A network protector comprising a network cir-= cult-breaker 6 and itsassociated control apparatus, is provided for controlling the flow of power In accordance with our invention, any suitable apparatus responsive to a groundv fault electrostatic relay 7 connected to the high voltage bank ,6 to the network 5.

5 reference to the capacitors 8, that the front con- 'tacts close in response to a ground on any single conductor of the feeder 3. Under such circumstances, of course the voltage to ground of the two ungrounded conductors is approximately 173% of normal. The back contacts of the relay 1 close in responseto a double-phase-to-ground fault or a three-phase fault on the feeder I.

A voltage-responsive relay 5 is provided for controlling the closure of the network circuit breaker 5. The voltage-responsive relay 9 is connected to output terminals of a voltage filter ii, to be energized in accordance with the positive symmetrical components of the polyphase voltage applied to the filter iii.

The phase sequence filter III is preferably of the type disclosed in the United States patent to B. E. Lenehan, No. 1,936,797, issued November 28, 1933, and assigned to the Westinghouse Electric 8: Manufacturing Company. This filter comprises an auto-transformer Illa, having a tap to provide a voltage less than half the total voltage impressed on the auto-transformer, for example, a 40% tap, and a reactor 10b and a resistor Me. The reactor Nb and resistor lIc are proportioned to produce, together, a 40% voltage drop lagging the impressed voltage angle of 60. Assuming that the phase rotation of the secondary voltages of the transformer bank I is as indicated by the subscripts a, b and c of the network conductors 5a, 5b and 5c, the coil of 8 is subject to a voltage equal to the vector sum of 40% of the A-phase delta voltage applied to the filter II, and a voltage equal to 40% of the C-phase delta voltage applied to the filter II but lagging the latter voltage by a phase angle of 60. As explained in the above-mentioned Lenehan patent, with such connections, the voltageresponsive relay 0 responds to .a positive symmetrical component of the polyphase voltage applied to the filter II. The relay 5 is preferably designed to close when the positive symmetrical components exceed a predetermined value, of the order of to of the normal phase-toground voltage of the network 5.

A transfer relay I l is provided for transfen'i s the C-phase connection of the filter I. from the network side to the transformer side of the network circuit breaker when the network 5 is deenergized. With this arrangement he filter II is energized in accordance with the polyphase secondary voltage of the transformer bank 5 when the network 5 is deenergized, and in accordance with a polypham system of voltages derived from both sides of the network circuit breaker 5 when the network 5 is energized. The phase voltages of the network 5 are, of course, referred to ground through neutral connections of other transformer banks (not shown) whenever the network 5 is energized. We do not claim the specific phasing method and apparatus disclosed herein as our joint invention, as such method and apparatus are covered in the copending sole application of M. A. Bostwick, Serial No. 716,819, filed March 22, 1934 and assigned to the Westington Electric 8: Manufacturing Company.

A lock-out relay I2 is provided for preventing; the energization of the voltage-responsive relay 9, after opening of the network circuit breaker I,

until the feeder 3 has been completely denergized by the opening of all other network protectors positive sequence.

the voltage-responsive relay I connected to the feeder. The lock-out relay I2 is designed to remain closed in response to all voltages above a comparatively low value such as 10% of normal, and to close at some higher value such as 60% of normal. As the reactances of the 5 usual network transformers are sufllciently'high to prevent the voltages on the network side from, fallingbelow something like 50% of normal in response to any faults on the feeder side, the lockout relay I! cannot drop out'in response to any fault to which the electrostatic relay 1 responds;

The operation of the apparatus shown in Fig. 1 may be set forth as follows: It is assumed that initially the source I is energized, and the network 5 is deenergized, and also switches and relays are in the positions shown in Fig. 1. In order to connect the source I to the network 5 to supply power thereto, the feeder breaker 2 is closed. Upon closure of the feeder breaker 2, voltage is impressed upon tors 8 and electrostatic relay 1, of-sufiicient value to cause the movable contact member of the relay 1 to assume its neutral position. The transformer bank I is energized from the feeder 3, and a secondary voltage appears across the input terminals of the phase sequence filter 10. Assuming that the connections of the feeder 3 are of proper phasesequence, the positive symmetrical components of the polyphase voltage applied to the filter l0 exceeds 95% of normal value, and the voltage responsive relay 9 closes. The relay 9 in closing, establishes a closing circuit for the network circuit breaker 5, and the latter closes to connect the secondary windings of the transformer bank 4 to the network 5, and also to comphase terminal of'the filter II from the feeder 1.;

side of the network circuit breaker 5 to the network side thereof.

If a fault occurs on the network 5, the voltage applied to the electrostatic relay 1 is not substantially affected, and the fault is burned off in the 50 usual'manner.

If a fault occurs on the feeder I, the feeder circuit breaker 2 trips open to interrupt the com nection of the source i, and also establishes an artificial ground through its back contact members 2a. In response to the artificial ground established by the feeder breaker 2, the electrostatic relay 1 closes its front contact members to trip open the network circuit breaker 6. In the case of'a ground fault, some of the relays 1 may open in response to the ground before the feeder breaker 2 opens. A similar action takes place with all other network protectors supplied from the feeder 3.

When the feeder 3 is completely deenergized by the opening of all network protectors supplied therefrom, the voltage applied to the lock-out relay l2 falls to zero and the lock-out relay l2 drops out to complete the circuit for the voltage responsive relay 9. The voltage responsive relay 5 does not-close at this time, however, as there is no voltage available at the terminals of the phase sequence filter lll.

Assuming that the network 5 is energized from other transformer banks (not shown), the trans- 75 that the various 15 the capaci- 2o g 2,020,981 fer relay H remains closed, thereby maintainingdescribed abo The feeder times of light load by merely opening the feeder breaker 2.

open.

Referring now to Fig. 2, the electrostatic relay 1 is shown in somewhat more diagrammatic form as energized by means of capacitors 8 in the same manner as in Fig. 1. The back contacts of the relay 7, however, are omitted, and in this arrangement the relay 1 responds only to single phase grounds.

In Fig. 3, three capacitors 8 of equal capacitance mal, the relay contacts will close under all ground its front contacts.

Fig. 6, shows an arrangement in which three 3 electrostatic relays-1, each arranged for undervoltage tripping,

30, and, of course, the capacitor I1 has a leading phase angle of former means, voltage-responsive electrostatic relay means connected to said feeder circuit responsive only to ground faults thereon for causing said circuit breaker to open, and means responsive to voltage conditions derived from said feeder circuit and said network circuit for causing said circuit breaker to reclose when said feeder circuit is energized and is free of incorrect phase connections as compared to said network circuit, whereby repeated opening and closing of said circuit breaker is avoided when said feeder circuit is ungrounded, regardless of the direction or magnitude of power flow through said circuit breaker.-

4. In combination with transformer means for supplying power from an ungrounded feeder circuit to anetwork circuit, a network circuit breaker for controlling the flow of power through said transformer means, fault-responsive means including an electrostatic relay energized from said feeder circuit and responsive only to ground faults thereon for causing said circuit breaker to open, and automatic reclosing means for said circuit breaker.

5. In combination with polyphase transformer means for supplying power from an ungrounded polphase feeder circuit to a polyphase network circuit, a network circuit breaker for controlling the flow of power through said transformer means, fault-responsive means including an electrostatic relay energized from said feeder circuit and responsive only to ground faults thereon for causing said circuit breaker to open, and means responsive to the positive symmetrical components of a polyphase system of voltages derived in part from both of said circuits. for causing said circuit breaker to close in response to a substantially normal relationship of voltages of said circuits.

6. In a network distribution system, a grounded-neutral source, a feeder circuit connected to said source, a feeder circuit breaker for controlling the fiow of power through said feeder circuit, a network circuit, transformer means for supplying power from said feeder circuit to said network circuit, said transformer means having ungrounded high voltage windings, electrostatic relay means connected to said feeder circuit and responsive only to a grounded condition thereof for causing said network circuit breaker to open means responsive to a fault on said feeder circuit 7 for causing said feeder circuit breaker to open,

and means effective when said feeder circuit breaker is open for establishing said grounded condition ,of "said feeder circuit, whereby said network circuit breaker opens only in response to a fault on said feedercircuit or the opening of said feeder breaker, regardless of the direction or magnitude of power flow therethrough.

'7. In a network distribution system, a ground- I edneutral source, a feeder circuit connected to said source, a feeder circuit breaker for controlling the flow of power through said feeder circuit, a network circuit, transformer means for supplying power from said feeder circuit to said network circuit, said transformer means having ungrounded high-voltage windings, pnase-toground voltage responsive means connected to said feeder circuit and responsive to a grounded condition thereof for causing said network circuit breaker to open, reclosing means 'for said networkcircuit breaker, lock-out means for pre- 10 venting reclosure of said network circuit breaker after opening thereof until said feeder circuit is completely deenergized, means responsive to a fault on said feeder circuit for causing said feeder circuit breaker to open, and means effective when said feeder circuit breaker is open for estabiishing said grounded condition of said feeder circuit, whereby said network circuit breaker opens only in response to a fault on said feeder circuit or the opening of said feeder breaker, and repeated opening and closing of said network circuit breaker is prevented during normal conditions and during fault conditions until said feeder circuit is completely deenergized.

8. In czmbination with a three-phase ungrounded circuit and means for energizing said circuit with three-phase voltage, electrorespon- 'sive means for detecting ground faults on said circuit comprising voltage-responsive means energized in accordance with the voltage between a single conductor of said circuit and ground, said voltage-responsive means including elements operable in response to both undervoltage conditions and overvoltage conditions.

9. The combination as defined in claim 8, in which the voltage-responsive means is an electrostatic relay having contacts operable in response to both undervoltage conditions and overvoltage conditions. v

10. In combination with a. three-phase un- 40 grounded circuit and means for energizing said circuit with three-phase voltage, electroresponsive means for detecting ground faults on said circuit comprising a pair of impedance means each having a terminal connected to different conductors of said circuit and having their free terminals connected together-to form a junction point, and an electrostatic relay responsive to the voltage between said junction point and w und.

11. The combination as defined in claimlO, in which the pair of impedance means is a pair of capacitors. Q

12. The combination as defined in claim 10, in which the pair of impedance means have abso- 5 'lute impedance values and impedance phase an- 

